Our research is focused on describing folding and unfolding intermediates in chromosome structure by analyzing changes in the structure of interphase chromosomes in G1 and G2 nuclei. We have carried out extensive serial section reconstructions using 40 nm sections from various stages of G1 and G2 nuclei. This has allowed a general survey of cell cycle changes. We are now beginning higher resolution EM tomography reconstructions to focus on particular folding stages identified by serial sectioning. Work at our university will focus on the internal structure of small folding units using reconstructions from thin sections at 120 keV. We are using IvEM to carry out EM tomography of thicker sections on the order of 0.5 um in thickness. Thicker sections are needed because we are interested in tracing the paths of 60-130 nm fibers which themselves are folded within interphase chromatids 0.2-0.4 um in diameter. We would also like to study the internal folding of 10-30 nm chromatin fibers within the larger 100-130 nm fibers themselves. Several reconstructions have been performed on datasets obtained with the "rEM with plans underway to obtain additional datasets.